The present invention relates to electrostatographic reproduction machines, and more particularly to an automatic document handler for use therewith that includes a sheet separator-feeder mechanism having a non-relative motion vacuum corrugating device which effectively prevents damage to images on document sheets being separated and fed thereby.
Generally, the process of electrostatographic production or reproduction of an image on a sheet of material is initiated by exposing a light image of an original image document onto a substantially uniformly charged photoreceptive member. The original image document may be manually placed, in registration, at an exposure station for such exposure, or it may be fed automatically by an automatic document handling device, also in registration, to the exposure station. Exposing the light image onto the charged photoreceptive member discharges areas of a photoconductive surface thereof corresponding to non-image areas in the original document, while maintaining the charge in image areas, thereby creating an electrostatic latent image of the image of the original document on the photoreceptive member.
Thereafter, developing material including charged toner particles is deposited onto the photoreceptive member such that the charged toner particles are attracted to the image areas on the photoconductive surface to develop the electrostatic latent image into a visible image. This developed image is then transferred from the photoreceptive member, either directly or after an intermediate transfer step, to an image receiving support substrate, such as a copy sheet of paper, thus creating a toner image on the support substrate corresponding to the original image of the original document. The image receiving support substrate, such as a copy sheet of paper, typically is fed automatically from a supply source, and in timed registration, to an image transfer station for receiving the toner image as such. Subsequently, the transferred image is typically fused and affixed to the image support substrate to form a permanent image thereon. In a final step, the photoconductive surface of the photoreceptive member is cleaned to remove any residual developing material thereon in preparation for successive imaging cycles.
It is known to employ in such an electrostatographic reproduction machine, an automatic document handler or handling apparatus as disclosed for example in U.S. Pat. No. 5,071,110. In such a machine, the automatic document handler automatically transports or feeds document sheets, one at a time, from a stack thereof to a registered position at an exposure station of the machine. With the advent of high speed electrostatographic reproduction machines, such an automatic document handler thereon must handle sets of simplex and duplex original image documents as above, for producing copies thereof at a rate in excess of a hundred simplex copies per minute. Usually, handling document sheets effectively at such speeds requires the use of a vacuum corrugating sheet separating and feeding device as disclosed for example, in U.S. Pat. No. 4,231,562; U.S. Pat. No. 4,305,576; U.S. Pat. Nos. 4,411,417 and 5,071,110.
For example, U.S. Pat. No. 4,305,576 discloses a typical vacuum separating and feeding system wherein a plurality of friction belts is arranged to run over a vacuum plenum placed at the bottom of a sheet supply tray which has a "U" shaped pocket formed in it. The pocket serves to provide space for the bottom sheet to be captured by the vacuum feed belt assembly, to provide an air seal between the bottom sheet and the edges of the pocket and to provide a high pressure seal between the bottom sheet and the remainder of the stack. This high pressure seal is achieved by supporting a major portion of the stack weight on the edge regions of the pocket.
In U.S. Pat. No. 4,411,417, the bottom sheet vacuum corrugation feeder includes a differently designed stack support tray that has a planar base portion defining a base plane, the front of the base portion having an opening within which the bottom sheet separator is positioned. The tray also includes two sloping planar side wings, one at each side of the opening in the base portion. The sloping planar side wings are angled upward from the base plane and are angled outward from front to rear of the tray and intersect the base plane such that the intersection at the rear of the tray is in the approximate location of the rear corners of a rectangle the size of a sheet to be fed.
Typically, such prior art is directed to devices including top or bottom sheet vacuum corrugation feeder trays which are used in combination with vacuum transport devices. Air injection means are provided to inject air between a sheet at end of the stack (top or bottom) and the remainder of a stack. A fixed position raised portion or corrugating member in the center of a vacuum plenum imparts a corrugation, that is, for example, U-shape, to a sheet when the sheet is pulled off the stack by a vacuum.
However, it has been found in some cases that original images on document sheets are damaged by such document sheet handling devices due to relative motion between the pulled off document sheet and the corrugating member, thus ordinarily resulting in poor quality copies.
Since the documents must be handled gently but positively to assure separation without damage through a number of cycles, a number of solutions have been suggested such as a separator-feeder mechanism that has a center belt which runs over the top of a fixed position corrugator or corrugating member. Such an arrangement with a fixed position corrugating member, is partially effective by eliminating relative motion between the belt and the sheet, however, it importantly does not eliminate relative motion between the corrugating member and the sheet. Additionally, such an arrangement has several other disadvantages such as the belt tending to wear relatively more rapidly due to the concentrated drag over the fixed position raised corrugator, and such as the belt tending to "dampen" the affect of the corrugator. In addition, the amplitude and shape of the corrugation on the sheet is limited by the ability of the belt which must track over the corrugator.